Research Content

Recent work includes the theoretical study of kinetic inductance under bias current. Traditionally, this has been calculated using BCS or Ginzburg-Landau theories with phenomenological assumptions, such as the "slow (fast) experimental scenario," where the superfluid density oscillates with (or remains frozen under) the electromagnetic field. Using the Keldysh-Eilenberger formalism, I avoided these assumptions and showed that only the "slow experimental scenario" is valid. This stems from the fact that in electromagnetic response under bias current, the Higgs mode (oscillation of superfluid density) must contribute. My work provides the first framework for calculating kinetic inductance under bias current using only microscopic theory, applicable across various temperatures, frequencies, and impurity levels.

Other research focuses on surface resistance in superconducting resonators, a key issue in superconducting devices. We calculated the low-frequency surface impedance of a dirty s-wave superconductor with an imperfect surface, modeled by a thin layer with reduced pairing or a proximity-coupled normal layer. Using Usadel equations, we derived the spatial distribution of the order parameter and quasiparticle density of states. The results show that engineering surface properties through pair-breaking mechanisms can optimize surface resistance, potentially reducing losses in resonators, strip lines, and RF cavities.

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